When you're a member of the royal family, there are a slew of rules, protocols and guidelines to follow. Everything from fashion, to food, etiquette is closely scrutinized by both the palace itself and royal-watchers.

And one of the things that is tightly regulated is PDA whilst on official business. If you haven't spent the last five years closely watching the every move of the Duke and Duchess of Cambridge, the general rule is they don't hold hands, kiss, or display any other form of physical affection, apart from the occasional hand on the back from Prince William.

In fact, in their five years of marriage, the Duke and Duchess have only ever been photographed so much as holding hands a handful of times. Once, when William led Kate out of Westminster Abbey by the hand (as is royal protocol), then when the two walked hand-in-hand to their awaiting helicopter to fly off to their honeymoon.

Those keeping an eye on royal-couple-to-be, Meghan Markle and Prince Harry, these past few weeks might have been shocked to see them acting very casually-holding hands, kissing each other on the cheek, and even stealing a kiss on the lips in the stands.

So why the double-standard? Why are Prince Harry and Meghan allowed to act out their various bouts of PDA, whilst Kate and Wills are confined to a formal foot of distance?

Well, it has to do with several things.

One: The Duke and Duchess are more visible

While Harry and Meghan are very much in the public eye and are hounded by paparazzi at every chance, they aren't quite in the position that Prince William and the Duchess are in. Eventually, William and Kate will be made King and Queen (Consort), and the sanctity of the monarch's station-which has rested safely with a very decorous and proper Queen Elizabeth II for upwards of 65 years-will fall to them. Therefore, unlike a rebellious younger brother, William and Kate must act every inch the royal couple all the time.

Harry, on the other hand, will be sixth in line to the throne after Kate's third royal baby is born, meaning that his position-while still extremely visible and important-is not quite as important. For example: Prince Andrew, the previous tenant of the sixth-in-line position, could walk hand-in-hand down a London street with anyone he wanted at this point, and very few would bat an eyelid.

Two: Prince Harry and Meghan Markle weren't "at work"

Although royal critics are quick to accuse the monarchy of "not doing anything," when they attend events, engagements and functions, the royals are very much "working." It is their job to attend events as representatives of the crown, which means that any PDA would be seen as inappropriate.

Harry and Meghan, however, were not at the Invictus Games in any official capacity. When Harry was there to open the Games and to meet with officials, he was "working," but when he was just attending games with Meghan, he was "off duty." Meghan, similarly, isn't a royal (yet), so she was not there on business-just for leisure.

Being "off duty" means that Meghan and Harry didn't technically have to act in any specific way because they weren't currently representing the Queen-they were just there as a couple.

If William and Kate ever attended an event outside of official business, they too would be allowed to hold hands and kiss-but whether they would or not is a separate question.

Three: The Duke and Duchess have less to prove

After five years of marriage and 2.5 kids, Kate and William are very much steady in their relationship. They're relatively unshakeable, and, as Robin Kermode, a body language expert, notes to The Independent, they "do not feel the need to prove their love".

"Some public figures use hand-holding as a deliberate act to prove that their relationship is solid, but this isn't something Prince William and Kate struggle with," reads the report.

And it's not as if Meghan and Harry are out to "prove" anything specifically, but they are in the early days of a relationship, where embracing and kissing your significant other is more common. Kate and Wills, after all, did too when they were in university.

And because Meghan is not yet an official member of the royal family, she doesn't really have to act in any certain way, unlike Kate, who is a Duchess.

Will Meghan and Harry's PDA continue the further they get to an engagement? Only time will tell.

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